Photoresist Processing Methods

ABSTRACT

A photoresist processing method includes treating a substrate with a sulfur-containing substance. A positive-tone photoresist is applied on and in contact with the treated substrate. The method includes selectively exposing a portion of the photoresist to actinic energy and developing the photoresist to remove the exposed portion and to form a photoresist pattern on the substrate. The treating with a sulfur-containing substance reduces an amount of residual photoresist intended for removal compared to an amount of residual photoresist that remains without the treating.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 11/510,010, filed Aug. 24, 2006, entitled“Photoresist Processing Methods”, naming Kevin J. Torek, Todd R. Abbott,Sandra Tagg, and Amy Weatherly as inventors, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

The invention pertains to photoresist processing methods, includingthose using positive-tone photoresist.

BACKGROUND OF THE INVENTION

Lithographic processes are widely used to selectively mask a portion ofa substrate, enabling processing of exposed portions of the substratewithout affecting the lithographically masked portion. Photolithographyuses a photoresist sensitive to actinic energy exposure. For apositive-tone photoresist, portions exposed to actinic energy arechemical modified as a result of the actinic energy exposure to becomemore soluble in a developer and are removed during subsequentdevelopment processing. Accordingly, interruptions in the chemicalmechanism rendering the exposed portions more soluble may preventremoval of desired portions of a photoresist. Accordingly, discovery ofresidual photoresist portions intended for removal may warrant revisionof standard processing techniques to accommodate special circumstancesthat generated the residue.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawing.

The FIGURE is a partial sectional view of an intermediate memoryconstruction showing residual photoresist intended for removal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aspects of the invention described herein originated during, but are notlimited to, fabrication of FLASH transistors used in NAND circuitry. TheFIGURE shows a partial sectional view of integrated circuit 10 whereinthe problem and its solution were discovered. Integrated circuit 10includes a substrate 12, which may be a semiconductor substrate. In thecontext of this document, the term “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove.

Silicon oxide formed by high density plasma (HDP) processing formsactive area isolation 14 in substrate 12. A layer of tunnel oxide 16containing SiO₂ is formed over substrate 12 followed by a layer of lowerpolysilicon 18 and a layer of upper polysilicon 20. A floating gate maybe formed in lower polysilicon 18 and upper polysilicon 20 inassociation with gate lines 36. A composite layer of gate dielectric 22formed over upper polysilicon 20 separates the floating gate from gatelines 36 and may be formed from conventional oxide-nitride-oxidematerials. A stack of materials forming gate line 36 includes a layer ofgate polysilicon 24 as the control gate, a layer of tungsten silicide 26as the gate conductor for programming a resulting memory cell, and alayer of silicon oxide 28. Silicon oxide 28 may be formed by chemicalvapor deposition using tetraethylorthosilicate (TEOS).

Integrated circuit 10 is at an intermediate step in processing whereincertain portions are masked with photoresist to allow selectiveprocessing of unmasked portions. Accordingly, the FIGURE shows aphotoresist 30 formed over portions of gate lines 36 and gate dielectric22. Notably, the FIGURE also shows residual photoresist 32 intended forremoval that remained after development processing. Dashed linesrepresenting a resist boundary 34 to designate the portion of residualphotoresist 32 intended for removal and the portion of photoresist 30intending to remain as a mask.

As indicated above, aspects of the invention are not limited to theparticular circumstances in which the problem and solution werediscovered. Using the disclosure herein, those of ordinary skill may nowappreciate other resist processing scenarios where a similar problem mayoccur and a similar solution may resolve observed defects in resistprocessing.

According to one aspect of the invention, a photoresist processingmethod includes treating a substrate with a sulfur-containing substanceincluding a surfactant having a sulfo group, a sulfur-containing plasma,and/or dimethyl sulfoxide (DMSO). A positive-tone photoresist is appliedon and in contact with the treated substrate. The method includesselectively exposing a portion of the photoresist to actinic energy anddeveloping the photoresist to remove the exposed portion and to form aphotoresist pattern on the substrate. The treating with asulfur-containing substance reduces an amount of residual photoresistintended for removal compared to an amount of residual photoresist thatremains without the treating.

By way of example, the surfactant that has a sulfo group may includeCF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃X, where X is H or NH₄, available from E. I.DuPont de Nemours in Wilmington, Del. as ZONYL™ FS-62, an anionicfluorosurfactant. A sulfo group is also known as a sulfonic acid grouptypically represented as —SO₂OH or —SO₃H. The sulfur-containingsubstance may also or instead include DMSO. The sulfur-containingsubstance may include sulfuric acid and hydrogen peroxide. Thesulfur-containing substance may be applied as a liquid, for example, byspin-on application or bath immersion. An aqueous solution containing0.02 to 3.0 volume percent (vol %) ZONYL™ FS-62 may be used, though a0.1 vol % solution was demonstrated to achieve the advantages describedbelow. An aqueous solution containing 0.1 to 100 vol % DMSO may be used,though a 1:10 DMSO:H₂O by volume solution was demonstrated to achievethe other advantages described below. A conventionally known “piranha”etch solution contains sulfuric acid and hydrogen peroxide, namely,generally greater than 80 weight percent (wt %) sulfuric acid and atleast some, but no more than 2 wt %, hydrogen peroxide with theremainder H₂O.

Although presently less preferable, a gaseous or a plasmasulfur-containing substance might be identified that also achieves thedescribed advantages. SO₂ gas treatment was attempted, but did notachieve the same effect as bath immersion in a piranha etch solution,ZONYL™ FS-62 aqueous solution, or DMSO aqueous solution. Even so, it isexpected that other sulfur-containing substances might be identifiedthat could be used in gas and/or plasma treatment to achieve similareffects.

The substrate may include a plurality of adjacent gate lines containingsilicon oxide over tungsten silicide over polysilicon, the gate linesbeing over a gate dielectric composite oxide-nitride-oxide layer whichis exposed between the gate lines. The gate lines and exposed portionsof the gate dielectric may be subjected to the treatment with asulfur-containing substance. Although the reason why aspects of theinvention described herein achieve the desired effect have not yet beendetermined, observation indicates that the topography and/or chemicalcomposition of the substrate on which the positive-tone photoresist isapplied appears to play a role in producing the residual photoresistintended for removal. Substrates with a different topography and/orchemical composition do not produce residual photoresist when processedin a similar fashion. Also, negative photoresists investigated thus fardo not produce residual photoresist. However, integrated circuit 10shown in the FIGURE clearly yields the problem of residual photoresistwhen a positive-tone, deep-UV photoresist available from Shin-EtsuMicroSi, Inc. in Phoenix, Ariz. known as SEPR-402 is used. Also, aspectsof the invention clearly resolve the residual photoresist problem.

A suitable solvent developer includes conventional tetramethyl ammoniumhydroxide (TMAH) at a concentration of 1 to 3 wt % in H₂O along with 100to 300 parts per million (ppm) of a conventional surfactant. Althoughthe mechanism involved in yielding residual photoresist is not wellunderstood, it is possible that the residual resist may be related touse of TMAH. The aspects of the invention allowed continued use ofexisting development processes without forcing replacement of TMAH byother less well known or effective developers.

The photoresist processing method may further include rinsing excesssulfur-containing substance from the substrate, if an excess amount ispresent, and applying the photoresist after the rinsing. Generally, H₂Omay be used for rinsing, however, other rinse agents may be warranteddepending upon the sulfur-containing substance applied.

Also, the method may further include, after treating the substrate,priming the substrate with an adhesion primer different from thesulfur-containing substance and applying the photoresist after thepriming. Use of adhesion primers is generally known to those of ordinaryskill and hexamethyl disilazane is a suitable primer. Notably, use ofHMDS for adhesion priming without treatment using a sulfur-containingsubstance still produces the problem of residual photoresist.Accordingly, observation indicated that conventional adhesion primingtechniques may be distinguished from aspects of the present invention.

Further, the photoresist processing method may include treating thesubstrate with a liquid containing sulfuric acid and hydrogen peroxidebefore treating with the sulfur-containing substance. That is, in thecircumstances where a sulfur-containing substance includes other thansulfuric acid and hydrogen peroxide, such as a piranha etch solution, itmay be advantageous to provide two treatment steps. The first step mayuse a piranha etch solution and the second step may use a differentsulfur-containing substance.

In addition to treatment with a sulfur-containing substance, the timedelay from the time the photoresist is applied up to soft baking (orpre-baking or post-apply baking) can also influence elimination ofresidual photoresist. Accordingly, the photoresist processing method mayinclude soft baking the photoresist after a delay of less than fiveminutes from the time the photoresist was applied, a maximum time delaydepending upon the sulfur-containing substance selected. Observationindicated that soft baking the photoresist after a delay of less thanten seconds from the time the photoresist was applied was sufficient toreduce defects caused by residual photoresist. The defect reduction wasequivalent to that obtained from a two-tank bath immersion in a piranhaetch solution. Unfortunately, some tools and processing schedulespreclude a less than or equal to ten second delay.

Treatment with a sulfur-containing liquid including sulfuric acid andhydrogen peroxide improved the maximum time delay to about 20 seconds.Treatment with a 1:10 DMSO:H₂O by volume solution improved the maximumtime delay to about three minutes. Treatment with a 0.1 vol % aqueoussolution of ZONYL™ FS-62 improved the maximum time delay to about fiveminutes. Accordingly, a robust photoresist processing method thatreduces the amount of residual photoresist intended for removal mayfurther include designating a maximum time delay depending upon thesulfur-containing substance selected.

According to another aspect of the invention, a photoresist processingmethod includes treating a substrate with a sulfur-containing substance,the substrate including silicon oxide, tungsten silicide, andpolysilicon all subjected to the treatment. A positive-tone photoresistis applied on and in contact with the treated silicon oxide, tungstensilicide, and polysilicon. The method includes selectively exposing aportion of the photoresist to actinic energy and developing thephotoresist to remove the exposed portion and to form a photoresistpattern on the substrate. The treating reduces an amount of residualphotoresist intended for removal compared to an amount of residualphotoresist that remains without the treating.

By way of example, the sulfur-containing substance may contain asurfactant having a sulfo group, a sulfur-containing plasma, sulfuricacid, and/or dimethyl sulfoxide. The particular compositions andphysical states for sulfur-containing substances described above may beused. Also, the substrate may exhibit the particular topographicalfeatures and compositions described above. Further, other additionalfeatures of the photoresist processing method described above may beincorporated. Still further, in the circumstance wherein thesulfur-containing substance includes sulfuric acid and hydrogenperoxide, the method may include additionally treating the treatedsubstrate with a surfactant having sulfo group, a sulfur-containingplasma, and/or DMSO.

According to a further aspect of the invention, a photoresist processingmethod includes treating a substrate with a sulfur-containing liquidincluding a surfactant having a sulfo group, sulfuric acid, and/or DMSO.The substrate includes a plurality of adjacent gate lines containingsilicon oxide over tungsten silicide over polysilicon, the gate linesbeing over a gate dielectric composite oxide-nitride-oxide layer whichis exposed between the gate lines. The gate lines and the exposedportions of the gate dielectric are subjected to the treatment. If anexcess amount of the sulfur-containing liquid is present, the methodincludes rinsing excess sulfur-containing liquid from the substrate.After the rinsing of excess sulfur-containing liquid, if any, thesubstrate is primed with an adhesion primer different from thesulfur-containing liquid. A positive-tone photoresist is applied on andin contact with the primed silicon oxide, tungsten silicide,polysilicon, and exposed gate dielectric. The photoresist is soft bakedafter a delay of less than five minutes from the time the photoresistwas applied, a maximum time delay depending upon the sulfur-containingliquid selected. A portion of the soft-baked photoresist is selectivelyexposed to actinic energy and the photoresist is developed to remove theexposed portion and to form a photoresist pattern on the substrate. Thetreating reduces an amount of residual photoresist intended for removalcompared to an amount of residual photoresist that remains without thetreating. By way example, the sulfur-containing substances, maximum timedelays, primer, and/or the additional treatment with a sulfur-containingsubstance more particularly described for the above aspects of theinvention may be incorporated.

Example 1

A silicon wafer including the intermediate memory construction shown inthe FIGURE was processed by priming the construction with vapordeposition of HMDS, spin-on coating the primed construction with aSEPR-402 positive-tone photoresist, soft baking the photoresist at 102°C. for 90 seconds after a delay of from 10 seconds to 5 minutes from thetime the photoresist was applied, selectively exposing a portion of thesoft-baked photoresist through a reticle with 248 nm radiation,post-exposure baking the photoresist at 110° C. for 90 seconds, anddeveloping the photoresist to remove the exposed portion and to form aphotoresist pattern on the substrate. Two applications of 4262 Developer(available from Fujifilm Electronic Materials of North Kingstown, R.I.)were used, each with a 30 second dwell time. All photoresist processingwas performed within the SEPR-402 manufacturer's specifications. Defectanalysis revealed the large number of defects indicated in the Table inthe “Control” column for Trial 1. Processing was repeated with anothersilicon wafer for Trial 2 shown in the Table. Trial 3 involvedre-analyzing the Trial 2 wafer with the system optimized to detectresidual photoresist. More than 99% of the defects for each trial wereidentified as residual photoresist.

Table of Examples 1-4 Results Trial Control Tool A Tool B Tool B (shortrinse) 1 51,544 85 73 94 2 11,147 22 44 23 3 22,977 113 123 112

Examples 2-4

The Example 1 trials were modified in Examples 2-4 by including two-tankbath immersion in a piranha etch solution before priming theconstruction. Example 2 was conducted in piranha Tool A while Examples 3and 4 were conducted in piranha Tool B. Each of the two piranha tanks inboth tools contained 90 wt % H₂SO₄, 3 wt % H₂O₂, and the remainder H₂Ocontrolled at 140° C. in the first tank and 120° C. in the second tank.The wafers were immersed for 10 minutes in each tank and then rinsedafter removal from the second tank. Even though the data is not reportedherein, it was discovered that the two 10 minute immersions producedless residual resist than two otherwise identical 5 minute immersions.Since Tool B had a more efficient rinse than Tool A, Example 4 decreasedrinse time to less than the Example 2 and 3 rinse time. Defect analysisrevealed a decreased number of defects indicated in the Table forExamples 2-4 respectively in the “Tool A,” “Tool B,” and “Tool B (shortrinse)” columns for Trial 1. Processing was repeated with anothersilicon wafer for Trial 2 shown in the Table. Trial 3 involvedre-analyzing the Trial 2 wafer with the system optimized to detectresidual photoresist. Even though the data is not reported herein, itwas discovered that the two 10 minute immersions extended the acceptabledelay to 20 seconds between photoresist coating and soft baking. Bycomparison, the Example 1 process required a delay of less than 10seconds to avoid residual resist.

Examples 5 and 6

Processing similar to that of Examples 2-4 was conducted for Examples 5and 6 except that respective solutions of 1:10 DMSO:H₂O by volume and0.1 vol % ZONYL™ FS-62 in H₂O were used instead of piranha etchsolution. Also, solutions maintained at ambient (about 20° C.) weresingle wafer spin applied with a dwell time of 45 seconds to 1 minutebefore spinning off the solution. No rinsing occurred. In Example 6, thedelay between photoresist coating and soft baking was 5 minutes. Thedecrease in residual resist defects was similar to that obtained for thepiranha etch solution. In Example 6, no residual resist defects wereidentified. Additionally, the 1:10 DMSO:H₂O by volume solution improvedthe coat-to-soft bake time delay to about 3 minutes. Treatment with a0.1 vol % aqueous solution of ZONYL™ FS-62 improved the coat-to-softbake time delay to about 5 minutes.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A photoresist processing method comprising: treating a sidewall surface of a gate line with a sulfur-containing substance including a surfactant having a sulfo group and/or including dimethyl sulfoxide, the sidewall surface of the gate line comprising at least one of tungsten silicide and polysilicon; applying a positive-tone photoresist on and in contact with the treated sidewall surface of the gate line; selectively exposing a portion of the photoresist to actinic energy; and developing the photoresist to remove the exposed portion and to form a photoresist pattern on the substrate, the treating reducing an amount of residual photoresist intended for removal compared to an amount of residual photoresist that remains without the treating. 2-5. (canceled)
 6. The method of claim 1 wherein the sulfur-containing substance comprises CF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃X, where X is H or NH₄.
 7. The method of claim 1 further comprising, if an excess amount of the sulfur-containing substance is present, rinsing excess sulfur-containing substance away and applying the photoresist after the rinsing.
 8. The method of claim 1 further comprising, after the treating, priming the sidewall surface of the gate line with an adhesion primer different from the sulfur-containing substance and applying the photoresist after the priming.
 9. The method of claim 1 further comprising soft baking the photoresist after a delay of less than 5 minutes from the time the photoresist was applied, a maximum time delay depending upon the sulfur-containing substance selected.
 10. The method of claim 1 further comprising treating the sidewall surface of the gate line with a liquid containing sulfuric acid and hydrogen peroxide before treating with the sulfur-containing substance.
 11. A photoresist processing method comprising: treating a surface of a substrate with a sulfur-containing substance, the treated surface of the substrate including tungsten silicide and polysilicon each simultaneously subjected to the treatment in contact with the tungsten silicide and polysilicon; applying a positive-tone photoresist on and in contact with the treated tungsten silicide and polysilicon of the surface of the substrate; selectively exposing a portion of the photoresist to actinic energy; and developing the photoresist to remove the exposed portion and to form a photoresist pattern on the substrate, the treating reducing an amount of residual photoresist intended for removal compared to an amount of residual photoresist that remains without the treating.
 12. The method of claim 11 wherein the sulfur-containing substance comprises a surfactant having a sulfo group, a sulfur-containing plasma, sulfuric acid, and/or dimethyl sulfoxide.
 13. The method of claim 11 wherein the sulfur-containing substance comprises CF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃X, where X is H or NH₄.
 14. The method of claim 11 wherein the sulfur-containing substance comprises a sulfur-containing plasma.
 15. The method of claim 11 wherein the sulfur-containing substance comprises sulfuric acid and hydrogen peroxide.
 16. The method of claim 15 comprising additionally treating the treated surface of the substrate with a surfactant having a sulfo group, a sulfur-containing plasma, and/or dimethyl sulfoxide.
 17. The method of claim 11 wherein the sulfur-containing substance comprises dimethyl sulfoxide.
 18. The method of claim 11 wherein the sulfur-containing substance is a liquid. 19-31. (canceled)
 32. The method of claim 1 wherein the sulfur-containing substance comprises dimethyl sulfoxide.
 33. The method of claim 1 wherein the sulfur-containing substance comprises a sulfo group.
 34. The method of claim 1 wherein the sulfur-containing substance comprises a sulfo group and dimethyl sulfoxide.
 35. The method of claim 6 wherein X is H.
 36. The method of claim 6 wherein X is NH₄.
 37. The method of claim 13 wherein X is H.
 38. The method of claim 13 wherein X is NH₄.
 39. A photoresist processing method comprising: treating a surface of a substrate with a sulfur-containing substance including CF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃H; applying a positive-tone photoresist on and in contact with the treated surface of the substrate; selectively exposing a portion of the photoresist to actinic energy; and developing the photoresist to remove the exposed portion and to form a photoresist pattern on the substrate, the treating reducing an amount of residual photoresist intended for removal compared to an amount of residual photoresist that remains without the treating.
 40. A photoresist processing method comprising: treating a surface of a substrate with a sulfur-containing substance including CF₃CF₂CF₂CF₂CF₂CF₂CH₂CH₂SO₃NH₄; applying a positive-tone photoresist on and in contact with the treated surface of the substrate; selectively exposing a portion of the photoresist to actinic energy; and developing the photoresist to remove the exposed portion and to form a photoresist pattern on the substrate, the treating reducing an amount of residual photoresist intended for removal compared to an amount of residual photoresist that remains without the treating. 